The present invention relates to fluid coupling devices of the type including temperature responsive bimetal elements, and more particularly, to a clip mounting arrangement for the free end of the element.
Fluid coupling devices of the type to which the present invention relates are now well known in the art and may be better understood by reference to U.S. Pat. No. 3,055,473, assigned to the assignee of the present invention. Although the present invention may be useful with many types and configurations of temperature responsive fluid couplings, it is especially advantageous on those to be used with vehicle radiator cooling fans, and will be described in connection therewith.
A typical fluid coupling device includes an output coupling member and a cover member cooperating to define a fluid chamber. The device includes a valve plate disposed to separate the fluid chamber into a reservoir and an operating chamber. An input coupling member is rotatably disposed within the operating chamber and the device includes valve means operable to control the flow of fluid between the reservoir and the operating chamber. The valve means includes a valve shaft extending outwardly through the cover means and being rotatable relative thereto. The rotational position of the valve shaft and the valve is controlled by a temperature responsive bimetal element having a first end portion connected to the valve shaft and a second end portion fixed relative to the cover means.
A problem which has arisen in connection with the use of viscous fluid couplings on four-cylinder engines relates to the greater vibration inherent in four-cylinder engines. The engine vibration is transmitted to the fluid coupling and typically, the result is excessive wear between the bimetal element and the shaft and between the bimetal element and its mounting bracket. If excessive wear occurs at either of these locations, there may be a substantial change in the temperature at which the coupling engages and/or disengages, causing unsatisfactory operation of the device.
If the wear becomes extreme, especially between the bimetal coil and the shaft, the coil may become completely detached from the device, with the result that the device will no longer be temperature responsive, but will remain either engaged or disengaged, whichever was the condition of the device at the time that the coil became detached.
A bimetal clip and assembly method capable of providing a more rigid mounting of the free end of the coil, without inducing unsatisfactory levels of hysteresis, is disclosed in copending U.S. application Ser. No. 909,755, filed May 26, 1978, and assigned to the assignee of the present invention. The invention disclosed in Ser. No. 909,755 includes a clip member of the type which may be used with the present invention, but with the clip member in direct metal-to-metal engagement with the free end of the coil. It has been found that, as a result of variations in the fit between the coil and clip, as will be illustrated hereinafter, the coil would sometimes be gripped too rigidly, causing breakage of the coil adjacent the clip, and would sometimes be mounted too loosely, resulting in wear between the coil and shaft as described previously.